Process for concentrating and purifying acetic acid from pyroligneous products



`C. C OUTOR PROCESS FOR CONCENTRATING AND PURIFYI 2,096,734 NG ACETIC Oct.. 26, 1937.

ACID FROM PYROLIGNEOUS PRODUCTS `Film1 May 18, 1934 Patented Oct. 26, 1937 L/Jl'trrrab 's-TATES..

PROCESS FOB CONCENTRAKTING AND PU- VBIFYING: ACETIC. ACID"FBOM PYBOLIG- 'Charles Coutor, Premery, France, assigner to Socity Etablissements Premery, France Lambioue Frei-es,

Application May 1s, 1934, semi No. 128,395 InFrance September 2, 1933 s claims.

Y It is well known to concentrate aqueous solu-v tions of acetic acid by distillation in the presence of auxiliary substances: Marckwald in the .year

1904 used xylol (D. R. P. No. 172,931); Evence I Coppee uses toluol, ethers, ketones (F. P. Nos.

558,875 and 565,265) and ever since a great many methods were proposed which employ certain ethers, ketones, wood oils and generally oxygencontaining substances. All these methods, which l apply satisfactorily to simple aqueous acetic acid solutions, entail serious disadvantages when acid from pyroligneous acid is treated, as the latter,

even after distillation, contains considerable amounts of more or less volatile impurities which u become concentrated with lthe acetic acid, a raw acid thus being obtained which is highly impure and thepurilcationl of which is very diilicult and costly. v

The object of this invention is a method which 20 is more advantageous than those already known and laccording to which the acetic acid from pyroligneous acid is puried and concentrated at the same time by the action of entraining or withdrawing substances, which generally consist 25 of a mixture of an oxygen-containingsubstance and a hydrocarbon, for reasons of efficiency.A

For instance, the mixture of butyl acetate and xylol, containing 20 to,50% xylol, may be used;

such a mixtureis a good solvent for acetic acid 80 and the oils in the pyroligneous acid and 'also forms with water lanjazeotropic mixture having a minimum loiline'point7 Anembodiment of the method comprising my invention, as well as `an apparatus` for carrying 35 it into practice, is diagrammatically illustrated by way of example in the drawing forming apart of the speciiication. v

The'de-alcoholized pyroligneousacid is introduced vthrough a pipe I into a still l which is 40 heated by a'steam coil. Thev acid may be dealc'ohollzed by any lmown method. `A portion of the tar contained in the pyroligneous acid, not being volatile at the temperaturev normally employed iny vaporlzing acetic acid, flows through 45 the pipe I6 whilethe vapors of the pyroligneous acid ow Vthrough the pipe Il and enter 4the dephlegmator 2. 'I'he pyroligneous acid vapor, as is well known, contains water "and fatty acids along withwood oils and tar. The dephlegmator 5 or column 2receives at the top through the pipe I8 a controlledstream or reflux of entraining liquid which has been decanted at the bottom of the column-3, as will be described in more detail later. The dephlegmator 2 functions to purify 55 the vapors of the pyroligneous acid by condensing the tar, wood oils and higher acids so that the product'issuingfrom the dephlegmator 2 through the pipe I9 and entering the bottom ofthe column 3 is essentially only a mixture of water vapor, acetic acid and vaporlzed entraining liquid. k5 y The entraining liquid entering the dephlegmator 2 will be vaporized'by the latent heat developedl by the condensation ofthe tar, woodoils and higher acids. l y

The tar, wood oils` and higher acids which are 10 condensed in the dephlegmatory 2 by the stream or redux of the entraining liquid will usually contain a small amount of water'and acetic acid. 'Ihe amount of the entraining liquid reux is so regulated as tocondensev atleast all-of the tar, wood oils, and the higher acids with a yminimumy quantity of water and acetic acid; This mixture containing the impurities ows through the pipe and is introduced into the top of a column 4 which is heated at 'theA bottom by a coil.r This 20 column removes from the tar,wood oilsaand higher acids, any water or acetic acid that mayhave 1 been returned through the pipe 20 'and 'returns thesame in vaporous form to the column 2 through the pipe 2l. Thev tar and Wood oils'are 25 collected at the bottom of ,column 4 and discharged through a pipe 22 and the higher'acids are drawn on through a pipe 23 and'c'ondensed in the cooler I3.

The puriiied vapors of pyroligneous acid enter the column 3 through the pipe i9 -where lthey ymeet on the plates of thiscolumn a reflux or the f fentraining or withdrawing'liquid which enters the column 3 through a'pipe -26 and whichdissolves' the acetic acid and allows the water vapor 35l to 'pass upward through the column in azeotropic vcombination with the entrainlng liquid. As the vapor passes upward through this column the amount of acid contained thereinis proportionately decreased and at the top of thecolumn 40 through a pipe 24 the azeotropic lmixture of entraining liquid and water having 4a minimum'boiling point is removed. Thisis' condensed at 3a and 3b and then' led through a pipe 25 to a decanter 5. 'Ihe latter permits the mixture to sep'- 45 arate into two distinct layers.` The entraining liquid ows back throughthe pipe 26 to thev top of the column 3 and the water flows through the pipe 26a. to the top of column 9 inwhich there I is removed the small amount of entrainingliquid (usually less than 2or3%) which is dissolved in l a water. 'Ihis entraining liquidU is recovered by causing steam to bubble` through it at the bottom of the column 9 andthe recovered 'vapors ofentraining agent ilow through kthe pipe21and into 55 the vapors exiting from the column 8 in the pipe 2l. 'I'he water is drawn oi! at the bottom of column 9 through a pipe 2l. This water will contain usually less than .03% acetic acid and chiefly formic acid.

The liquid at the bottom of the column 3 constitutes two distinct layers: a layer of the entraining or withdrawing liquid which is returned through pipe i8 to form the stream or reflux for the dephlegmator 2 as described above. and a layer of aqueous solution of acetic acid. the strength of which is not over 45%. I'he concentration of the acetic acid is not permitted to exceed this gure and as a consequence the acid and the entraining liquid will separate in distinct layersI and also only a small amount of entraining liquid will be dissolved in the acetic acid.

'Ihe acid solution is-drawnoii' througha pipe 29 and introduced into the top of the columnv t heated at the bottom by a steam coil. In this column the acid is dehydrated by rectication and the vapors in the column which are poorer in acid than the liquid in pipe 29 are sent back to the column 3 through pipe 3l. Any entraining liquid dissolved in the acid and returning to the column 6 is vaporized in the upper portion of this column.` A thermostatio regulator ta actuated atone of the plates of column l controls the heat applied at the bottom of the column. 'I'his is usually controlled so that the temperature is around 108 C. near the middle of the column. 'I'he concentrated acetic acid in the form of vapors at the bottom of column e or a few plates above is removed through a pipe Il and condensed in the cooler 1. This acid is substantially anhydrous and colorless and is the s0- called technical acetic acid which is suitable for most industrial purposes. It will contain a small amount of formic acid but only tracesioi' higher acids. a f

In order to avoid accumulation in the bottom of the column 6 oi' certain impurities which are but slightly volatile and which wouldform resins on the heating coil, a small quantity of the liquid is withdrawn through a pipe I2 and a greater part of this liquid is vaporized yin the heater 8 which sends its vapors back to the col- Vumn 8 through pipe I3. The impurities are discharged through the pipe 24 to the tar column I. If a so-called tasteful" (edible) aceticacid is desired, the vapors are sent from the bottom` of the column 6 through a pipe to the bottom of the rectifying `column il, the reiiux of which returns to the columnr 'through the pipe 36. At the bottom of column `Ii an acetic acid which is rich in formic acid is withdrawn through the pipe 3l.Y The pure acidV is withdrawn through the pipe `38 from a plate located near the top of the column. This acid issent to the top of column i2 which removes an additional quantity of formic acid from the product and sends the formic acid vapors through a pipe Il to the column ll. The ytasteful acetic acid is taken from the base of the column I2 through a pipe 40 and thisacid is condensed in a cooler il.

The entraining liquid may become slightly modied during use and it is advantageous to eliminate the products in the entraining liquid which would progressively increase the steam consumption. `To accomplish this, a small quantity of the entraining liquid is drawn oil' through a pipe ll and introduced into a rectifying column I0 heated by a steam coil. 'I'he impurities pass to the condenser I 0o through a pipe 42 and the yligneous acid may also be distilled together .with

its tar without inconvenience.

It is advantageous to preparatorily free the pyroligneous acid from its wood alcohol content.

The dephlegmator 2 utilizes part of the entraining liquid which is recycled automatically as a result of the dehydration. An adjustment of` the amounts thus recycled into the dephlegmator 2 will sufiice to keep the concentration of the` aqueous phase streaming towards 6 from exceeding ya definite limit.

It will be appreciated that the purification is costless as far as heat is concerned,-because they heat 4required to vaporize the entraining liquid in the dephlegmator 2 is provided by the condensation of the tar, wood oils and higher acids.`

. 'I'he entraining liquid lends itself to high-teinperaturedecantation (89 CJ: the connections fromr the decanter to the condenser malle.- it possible, whereby the expenditureat the bottom of columns land 6 is limited to the mere vaporization of the entraining liquid decantedat l. Where tasteful acetic acid is produced it is suitable to heat the recovery column 9 with the aid of column il from the top of which the vapours issue at about 107 C.; the columns `I2 and l may also be arranged above each other, so that some steam may be spared.

In no instance the expenditure to obtain tasteful acid will be higher than twice the steam necessary. to vaporize the pyroligneous acid, even if the concentration of the same should' be as highasl5percent. .a f A It is unimportantthat the pyroligneous acid is taken in at the bottom of column 2 in the liquid instead of the vapour phase; it is only necessary then to suitably design the heater for column 4, in order that the pyroligneous acid may be inthe training liquid in thedephlegmator 2.

, 'I'he use of the butyl lacetate-xylol mixture as Y I mentioned above is not limitative and the principle of the invention is not modified by vthe use of any otherasuitable mixture. An oxygen-containing substance and a hydrocarbon willpreferably be chosen; for instance, a mixture of mesityl oxide with a petrol boiling from about to C. is quite suitable.

The expression"entraining liquid used herein refers to a stable, non-reactive liquid or mixture of liquids having the property of forming an azeotropic mixture with water in the presence of acetic acid. 'Ihe'materials suitable for this purpose are well known in the'prior art and the requirements for such an entraining liquid are set forth in detail in French Patent No. 622.680. v Generally speaking, the oxygen-containing substance imparts solving properties to the auxiliary mixture, while the hydrocarbon will decrease said properties somewhat at the same time as they will trated acid present at the bottom of I.

the wood oils. higher acids, and remaining tar r contained therein and simultaneously to vaporize said entraining liquid by the latent heat o! vaporization given up bythe condensed products, and contacting the pui-ined vapors with an additional quantity of the same entraining liquid to dehydrate the acid by azeotropic distillation, the said entraining liquid being one adapted to form withy water an azeotrope of minimum boiling point. g

Y 2. In a process i'or the separation of a substantially pure anhydrous acetic acid from de-alcoholized pyroligneous acid the steps which .comprise `vaporizing the pyroligneous acid to eliminate the bulk of the tar, contacting said pyroligneous acid in a vapor phase with a water entraining liquid introduced as a reflux and controlled in amount to condense the wood oils, high.

er acids, and remaining tar contained therein and simultaneously to vaporize said entraining liquid lby the latent heat of vaporization given up by the condensed products, and contacting the purifled vapors with an additional quantity oi the y same entraining liquid 'to dehydrate the acidbyA azeotropic distillation, the said entraining liquid being one adaptedV to form with water an azeotrope of minimum boiling point.

3. In a process for the separation of a substantialLv pure anhydrous acetic acid from de-alcoholized pyroligneous acid the steps which comprise vaporizing the pyroligneous acid to eliminate the bulk-of the tar, contacting said pyroylignecus acid in a. vapor phase with a water entraining liquid introduced asa reiiux and controlled in amount to condense the wood oils, higher acids, and remaining tar contained therein and simultaneously to vaporize said entraining liquid bythe latent heat of vaporization ,given up by the condensed products, and contacting the puriiied vapors with an additional quantity of the same entraining liquid to dehydrate the acid by 4itzeotropic distillation, the entraining liquid used in the condensation of the impurities being ob tained from a point in the dehydrating operation and being one adapted to form with water any azeotrope of minimum boiling point.

4. In a process for the separation of a substantially pure anhydrous acetic acid from de-alcoholized'pyroligneous acid the steps which comprise vaporizing the pyroligneous acid to eliminate the bulk of the tar, contacting said pyroligneous acid in a vapor phase with a. water entraining liquid introduced as a reux and controlled in amount to condense the wood oils, higher acids, and remaining tar contained therein andslmultaneously to vaporize said entraining liquid by the latent heat of vaporization i given up by the condensed products, and contacting the puried vapors with an additional" quantity o1' the same entraining liquid to dehyfV drate the acid by azeotropic distillation, the eni training liquid used in the condensation of the impurities being obtained from a point in the dehydrating column and being one adapted to form with water an azeotrope of minimum boiling point." c l 5. The process described in claim 2 m which the entraining liquid comprises a mixture of butyl' oxide and a petrol boiling from 125 to 135 C. l

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